1. Field of the Invention
This invention relates to the field of multiple speed ratio transmissions. More particularly, the invention pertains to an apparatus and method for changing speed ratios in such a transmission by slowing a gear through selectively operated clutches. This invention pertains to the field of synchronized shifting among the various speed ratios of a multiple speed tractor transmission.
2. Description of the Prior Art
In multiple speed ratio transmissions of the type that employ synchronizers to driveably connect selected gears to a shaft, the synchronizers are forced first toward the gear to be connected to engage frictionally the gear with a conical surface on the synchronizer. This process, called synchronization, brings the shaft, synchronizer and gear to approximately the same speed before the gear is connected mechanically by engagement of splines on the synchronizer sleeve with dog teeth on the gear. The surfaces of the components that are forced frictionally into contact to produce the synchronism are conical. Therefore, the axially directed force required to move the synchronizer sleeve has only a minor component in the radial direction to develop the frictional engagement on the gear. The amount of shifting effort in moving the synchronizer from the neutral position to the engaged position varies, therefore, in accordance with the amount of braking force that must be applied to the gear before the speeds are made up synchronous. Furthermore, reflected inertia on the gear, in addition to its own inertia, must be accomodated and includes the inertia of the rotating components that remain driveably connected to the gear during synchronization. The effective rotational inertia of the gear can be very large, especially where speed reduction gearsets located partly on a countershaft are employed. The reflected inertia of these components adds to the inertia of the gear and must be slowed by the synchronizer prior to driveably connecting the gear to the shaft. Speed reduction gearsets amplify the amount of inertia that is applied to the gear connected by the synchronizer.
The amount of shifting effort required of the vehicle operator to connect the gear to the shaft through the synchronizer should be kept as low as possible. It is preferred in making shifts of this sort, through operation of a synchronizer, that the gear be driveably disconnected from the source of power before synchronism is attempted to keep shifting efforts at a minimum.
Occasionally in making upshifts among gear ratios in a tractor transmission that has the capacity to produce a large number of speed ratios, a gear to be connected to a shaft by a synchronizer turns at a substantially higher speed than the speed of the shaft. Conventionally, substantially greater effort is required to move the synchronizer to the engaged position in order to slow the gear and overcome its inertia and the inertia of the components that are driveably connected to the gear.